Before & After High Pressure Washdown & Seal of Sand Rendered Home in Kalamunda

If you’ve made it this far through our website, you’ve probably seen some photos of this one. We just love the stark difference between the before and afters, and on such an impressive looking house too. Here’s what we did:

The sand render that gives this house it’s Tuscan look is very porous, particularly compared to a modern acrylic render. Kalamunda winters are very wet and with the amount of foliage and shade in this leafy area, a porous surface doesn’t get much chance to dry. As Spring emerges, it gets a few months of being warm and wet, leading to huge amounts of growth.

The owner was looking at a potential cost of $30,000 to get the house re-rendered and was understandably looking for a more cost effective alternative.

house in Kalamunda covered in growth and staining

We offered to chemically treat and pressure clean the entire external area of the home as a cheaper alternative, to see if we would be able to prolong or entirely avoid such a substantial cost to the client. We were also hired to apply a sealer to the entire external area of the house.

The nature of the work was straight forward in that it was the one type of surface and growth across the whole area, but it had a few potential problems. Being an older sand render, it was not only porous but very brittle and easy to damage. We had to get the right balance of enough flow rate and pressure to remove the dirt and growth, without blasting the render right off.

corner shot of house covered in growth

We used a Sodium Hypochlorite, Potassium Hydroxide and surfactant mix as a strong pre-treatment, so that we would be able to minimise the exposure to high pressure. Sodium Hypochlorite and Potassium Hydroxide are both strong oxidising agents which attack the cellular structure of the growth, making it easier to come out. The surfactants simply allow for better penetration, so that the oxidisation is occurring at the root/hyphae level, so that we’re removing the whole structure, not just skimming the top and leaving the roots where they may be able to survive and cause regrowth. The solution is also buffered, so that it slows the reaction, allowing it to penetrate, rather than reacting quickly and consuming itself at the surface.

Once the chemical pre-treatment had been applied, kept wet and allowed to work, it was simply a matter of pressure cleaning the whole house in small sections with a turbo nozzle.

house in kalamunda being pressure washed with turbo nozzle

Once the house was clean and free from growth, there was still a lot of residual green staining as expected. If we had tried to remove this with pressure cleaning alone, we would have stripped the render. Instead we applied a bleaching solution to the entire house over a few days. This removed the staining, but is also something we do regardless of any discolouration. Aside from sealing, our best bet to prevent growth is to kill any remaining spores or hyphae, so that the growth doesn’t rear it’s ugly head again, as soon as there’s rain.

half of house being cleaned

We advised the client that we couldn’t be certain how well a penetrating sealer would work on a vertical porous surface such as this. A Fluoropolymer sealer would have provided the best chances for protection, but as this was an uncommon application it seemed like too great of an expense without guaranteed efficacy. After speaking to the client about their needs, we settled on a water based Silane/Siloxane penetrating sealer to offer reasonable protection, at a much more affordable price, given the size of this house.

We had a lot of fun getting the photos on this one.

kalamunda house after being pressure cleaned